Enhanced TOC removal from paper mill wastewater using air dielectric barrier discharge plasma with persulfate sources: Mechanistic insights and continuous flow operation performance evaluation

This study investigates the removal of total organic carbon (TOC) from paper mill wastewater using air dielectric barrier discharge (DBD) plasma, combined with various persulfate sources, namely potassium peroxymonosulfate (PMS), potassium peroxydisulfate (PDS), and sodium persulfate (SPS). Mechanistic insights into the activation of plasma-PDS and -PMS were obtained through quenching experiments and electron spin resonance (ESR) techniques. The addition of persulfate to air DBD plasma increased TOC removal kinetics by approximately 1.7–3 times, with plasma-PDS exhibiting the highest synergistic factor of 3.14. The electric field from the plasma significantly enhanced radical production, with plasma-PDS outperforming plasma-PMS due to its higher generation of sulfate (SO₄^•−) and hydroxyl radicals (•OH), which are more effective at breaking down complex organic compounds in paper mill wastewater. In continuous-flow experiments, the plasma-PDS process with 10 mM and a 90-minute retention time achieved a 94.5% TOC removal efficiency for actual paper mill wastewater over 8 h operation, demonstrating its effectiveness and stability for extended treatment. Quenching experiments revealed that electrons play a key role in PDS activation, whereas ¹O₂ is crucial for PMS activation.